The present invention relates to a new and improved method of, and apparatus for, converting a binary signal.
In its more specific aspects, the present invention particularly relates to a new and improved method of, and apparatus for, converting a binary or first signal which assumes a first state and a second state, into a pulsed or second signal. The method is preferably used for recording binary signals on a magnetic record carrier.
Binary signals are widely used in the field of electrical signal processing. Signals in the form of modulated binary signals are known and such signals contain pulses of substantially equal length or time duration and which pulses follow each other at different spacings or intervals. Other modulated binary signals possess pulses whose length or time duration is not constant. With respect to the last mentioned signals it is important to recognize the beginning and the end of the pulse, that is, the edges or flanks of each pulse. During the digital recording of such signal on a magnetic tape, there are thus recorded pulses by supplying a corresponding writing current to a recording head. In this manner, the polarity of the magnetization on the magnetic tape is changed along the length of the magnetic tape such that an image or copy of the current pulses supplied to the recording head is formed. A region on the magnetic tape having a specific length and a magnetization of a particular polarity, corresponds to a pulse having a specific length or duration. Another region on the magnetic tape having a specific length and a magnetization of a different polarity, corresponds to a pulse which is not present, that is, an interpause or section between two consecutive pulses. Therefore, the edges or flanks of the pulses effect a change between the polarities on the magnetic tape. In the recording head, this means that the writing current for the pulses once flows in one direction and then in the other direction. On the average, when considered over a longer time period, there thus flows a specific current in the recording head and this current flow also causes heating-up of the recording head.
It is one disadvantage of this known construction that, when processing such binary signals in, for example, recording heads provided for a plurality of tracks on the magnetic tape, the writing currents associated with all of the tracks conjointly heat up the recording heads. This stronger heating action reduces the working or operating life of such recording heads or components. The writing current, however, also produces a power loss or dissipation in the writing head electronics with which the recording head is series connected.
In a method and an apparatus such as known, for example, from U.S. Pat. No. 4,562,491, granted Dec. 31, 1985, signals are processed for recording in a plurality of tracks on a magnetic record carrier. This is effected by converting the individual pulses of an input signal into a variable number of very short pulses. Two polarities are provided for the short pulses. Short pules in the recorded signal are associated with the edges or flanks of the pulses of the input signal and the short pulses are offset from each other when they are recorded on adjacent tracks of the magnetic record carrier.
It is one disadvantage of this method that there are permitted to be processed for recording only those input signals whose edges occur at particular previously-known positions or whose pulse lengths or durations have only certain discrete values. This means that there exists a predetermined raster in which these pulse edges can occur and in which the short pulses derived from these pulse edges can be positioned. Consequently, also the short pulses may possess only predetermined mutual spacings. The processing of input signals which are modulated with respect to their pulse length or duration, is impossible in this known way. Only specific binary signals can be so processed for recording.